Ion flux promotes heart and endoderm lateral asymmetry in Ciona intestinalis

Date of Award

Spring 2017

Document Type

Restricted Thesis

Terms of Use

© 2017 Karl H. Palmquist. All rights reserved.

Degree Name

Bachelor of Arts

Department

Biology Department

First Advisor

Bradley Justin Davidson

Abstract

Diverse bilaterian body plans are commonly characterized by a striking asymmetry along the left-right (LR) axis. While the TGFβ-family member, Nodal, is thought to play a highly conserved role in this process, the impact of other mechanisms on LR asymmetry is poorly characterized. To better understand what other mechanisms contribute to asymmetric organogenesis, we employ the tunicate Ciona intestinalis. We have found that the Ciona heart and stomach are positioned on the right side of developing juveniles. Asymmetric positioning of these organs is first observed during late embryonic stages. Intriguingly, we show that Nodal signaling is dispensable for heart lateral asymmetry in larvae. Through inhibitor experiments, we have found that H⁺/K⁺-ATPase dependent ion flux is necessary for proper heart and endoderm lateral asymmetry in both larvae and juveniles. Based on our findings, we propose that ion flux regulates PCP during Ciona neurula stages. Our data support a dual role for ion flux-dependent PCP. First, ion flux-dependent PCP controls cilia polarization, subsequent neurula rotation, and chorion-dependent asymmetric signaling. Second, ion flux-dependent PCP drives tissue-intrinsic cytoskeletal polarities, which result in endoderm lateral asymmetry. In both cases, asymmetric endoderm morphogenesis promotes heart lateral asymmetry. These results provide key insight into the evolution of LR patterning mechanisms and further inform our understanding of recent Nodal-independent lateral asymmetry mechanisms in vertebrates.

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